This application relates to and claims priority to corresponding German Patent Application No. 100 16 925.2, which was filed on Apr. 5, 2000, and which is incorporated by reference herein.
The invention relates to an iris diaphragm, in particular for an exposure lens in semiconductor lithography.
In previous iris diaphragms, including the case of iris diaphragms for exposure lenses in semiconductor lithography, changes in diameter of the diaphragm aperture are achieved by an oscillating movement. The change in diameter is carried out in this case by a multiplicity of leaves which are each mounted with one end in a so-called diaphragm base and with their other end respectively in a grooved ring. The leaves are curved like sickles, and an oscillating drive device guides the leaves, depending on the direction of rotation, more or less deeply in the fashion of a chord into the diaphragm aperture, the light beam passing through being cut as a result.
Together with the loads it produces, the oscillating movementxe2x80x94in which not inconsiderable masses are to be movedxe2x80x94has a disadvanatageous effect on the service life of the iris diaphragm. This holds, in particular, when high cycles obtain as is the case, for example, with an exposure lens in semiconductor lithography.
It is therefore the object of the present invention to create an iris diaphragm of the type mentioned at the beginning which has a long service life, in particular which operates precisely and with low wear even for high opening and closing cycles of the leaves.
This object is achieved according to the invention by the features named in the characterizing part of claim 1.
Instead of an oscillating movement, a linear or continuous rotary movement is achieved with the aid of an inherently closed circumferential track by the inventive configuration of the grooved ring with the useful-region curves and the return curves in the selected configuration. By comparison with an oscillating movement, a continuous rotary movement exerts substantially less load on the parts participating in the movement.
In one configuration according to the invention, it can be provided that the return regions are designed at least approximately as multinomials. By using a multinomial, it is possible to create a high degree of freedom from forces during the rotary movement, very fast switching movements thus also being possible for the purpose of adjusting the leaves. A smooth transition, and thus a smooth force profile without jumps, are achieved by the multinomial according to the invention.
In a further configuration of the invention, it can be provided that the leaves are each provided with a bearing via which they are respectively guided in the circumferential track, a high degree of freedom from friction being achieved upon use of the bearings as antifriction bearings, something which was not directly possible in the solution according to the prior art.
In a very advantageous configuration, it can be provided in this case that each leaf respectively has two antifriction bearings in the manner of a parallel guide.
Since the leaf sheets are generally relatively thin and therefore correspondingly at risk in the case of fatigue loading, the bearing according to the invention can deliver a higher level of dependability and thus a longer service life.
A very advantageous development of the invention can consist in selecting the rotary drive direction of the drive device and the courses of the useful-region curves and of the return curves such that upon opening of the diaphragm aperture in the track regions of the return curves a tractive force is exerted on the leaves.
This directional force according to the invention is opposite to the direction of movement of the prior art, a tractive force being exerted on the leaves when the diaphragm closes. Specifically, so-called parallel curves are obtained in this way during the oscillating movements, as a result of which it is easier to master the forces acting on the leaves and the rivets via which the leaves are connected to the grooved ring and the diaphragms.
Although the solution according to the invention in the useful-region curves does now entail a somewhat poorer force profile, because of the possibility of more effectively bearing the leaves, for example with the aid of antifriction bearings, and the continuous rotary movement, this is possible without difficulties. On the other hand, a better force profile is achieved by this course of movement in the return curves.
For assembly reasons, it can be advantageous for the useful-region curves or the return curves to be designed as continuous slots in the grooved ring.